Question: $(\sin^2 \theta + \cos^2 \theta)(\cos\theta) = \; ?$
Solution: We can use the identity ${\sin^2 \theta} + {\cos^2 \theta} = 1$ to simplify this expression. $1$ ${\sin\theta}$ ${\cos\theta}$ $\theta$ We can see why this is true by using the Pythagorean Theorem. So, $(\sin^2 \theta + \cos^2 \theta)(\cos\theta) = 1 \cdot \cos\theta = \cos\theta$